Non-Hodgkin's lymphoma (7.4 per million children aged under 15) represents 6% of all childhood cancer. In contrast to the adult forms of NHL, children most commonly develop T-cell (lymphoblastic) lymphoma or small, non-cleaved follicular B-cell tumors. Three recent lines of research have served to focus attention on lymphomas (1) modern cytogenetic techniques have linked some types of NHL, notably Burkitt's lymphoma, to a specific oncogene and to immune-related genes (2) interest in viral causes of lymphoma - well-established through the research on Epstein-Barr virus and African Burkitt's lymphoma - has been stimulated by recent data on the human T-leukemia virus and by the association of lymphoma with a presumed transmissable AIDS (acquired immune deficiency syndrome) agent (3) monoclonal antibodies provide a new and powerful means of classifying lymphomas according to their expression of surface antigen, which reflects their lineage and degree of differentiation. The major aims of the study are to characterize childhood NHL with report to chromosomal abnormalities and immunologic phenotype, and to relate the findings of these studies to etiologic factors derived from case/control interviews and viral studies. The interviews will focus on immune-related disorders in the family of the patient, and unusual or chronic antigenic exposures of the patient. Viral studies will examine the role of EBV and HTLV-related viruses and will search for previously unrecognized retroviruses in the tumor tissues. Incident cases of NHL, enrolled on therapeutic studies of the Children's Cancer Study Group, will be eligible. Biopsy material from these children will be used for cytogenetic analyses, cell surface marker studies, histopathology, and viral studies. Serum will be tested for specific viral antibodies, and some serum and tumor tissue will be frozen for future use. The mothers of cases, and a matched control group selected by random digit dialing, will be interviewed by telephone to provide data on familial associations, particularly of immune-related conditions such as autoimmune disease and allergy, and on environmental exposures of the child and parents. It is hoped that this study will provide a clearer understanding of the interrelations of viruses, chromosomal abnormalities, and genetic and acquired immune function disturbances in childhood NHL.